Tires vs. drag chain.

I had time to check out just how conductive combine tires are, whether they insulate, and whether the drag chain helps, hinders, or is mostly psychological. Here is what I found:

Front tires are bias ply 30.5 X 32 and the rear tires are 16.9 X 26. I ran the front tire onto a sheet of bright, untarnished copper and one lead of a Fluke 77 VOM to the copper sheet and the other to one of the lug bolts of the rim. In order to confirm that readings didn't reflect capacitively charging the machine and affecting the reading, I took readings with leads first connected one way and then the other. There was no noticeable difference in the resistance readings that was dependent on the polarity of the test probes. The readings also remained constant, indicating no capacitive charge or discharge. Front tire lug bolt to sheet reading was 97 KΩ. When I moved the combine to place the rear tire on the copper sheet, I got a value of 350 KΩ for the back tire. That gives us two paths with a resistance of 97K and two with a resistance of 350K. If I remember my basic Ohms Law, to find the value of resistors in parallel you sum the reciprocal of all the values and then find the reciprocal of that number to determine total resistance. I came up with 37.975 KΩ from combine frame to ground. If you consider that walking across a carpet in a dry room will charge your body to about 35,000 volts, then the path to ground offered by the tires would let nearly 1 amp of current pass at that voltage level.